The present invention relates to thermal protectors and more particularly to thermal protectors having at least one thermally responsive bimetal blade which is designed to be reset after opening by removing an impressed voltage, thereby allowing the blade to cool and close.
Generally, thermal protectors of the type described herein have a stationary electrode and a movable electrode. The movable electrode is responsive to heat and generally takes the form of a bimetal blade. When the ambient temperature rises to a predetermined level, the movable electrode distances itself from the stationary electrode and interrupts the current to the load that is being protected. The load is connected to a power source through the thermal protector. These types of safety devices are generally used to prevent overheating of various types of electrical machinery, equipment and circuits.
Of the bimetal thermal protectors, resetable types have been disclosed where the movable electrodes are bridged with a heat sensitive resistor, generally in a manner such that the resistor is inserted into a recess in the movable electrode or is disposed around lead-in wires that extend within the envelope. An example of the latter type of protector is shown in the U.S. Pat. No. 4,287,500 to Ueda, which discloses the use of a PTC heater inside of a bulbous envelope to keep a bimetal blade open after it has opened initially. The bimetal blade stays open until the entire protector is removed from the circuit and/or the current to the load is terminated.